The use of liquid immersion for projecting or exposing film has been known and used in the industry for more than two decades. The film is immersed in a transparent liquid having an index of refraction approximately equal to that of the film, and the resulting image is then minimized with respect to the effects of optical imperfections in or upon the film. Apparatus that has been used for this purpose falls generally into three categories, which will be briefly described.
One category of apparatus is the "thin layer" type of machine. The film passes between a pair of pads or applicators which are continuously wetted with the liquid or solvent, thereby applying a thin layer of the liquid or solvent onto each surface of the film. The film remains wetted until it passes by the aperture where exposure or projection takes place, and then the liquid is evaporated before the film is rewound into a roll or reel.
Another type of apparatus is the "total immersion" machine. A large body of liquid not only immerses the film gate that provides the aperture for projection or exposure of the film, but the film is also totally immersed in the liquid for some distance before reaching the aperture. This type of apparatus has been used for some time in step optical printers or projectors. It has only very recently been incorporated into machines in which the film runs continuously, rather than being stepped. Such a liquid immersion machine of the continuous type is shown, for example, in the copending application of the present applicants Ser. No. 791,135 filed Apr. 26, 1977 and now U.S. Pat. No. 4,105,329.
A third type of liquid immersion apparatus is the "aquarium gate", also known as the Ott gate. This gate is constructed with a parallel pair of blocks or panels or glass, with a space between them through which the film passes. A light beam for exposing or projecting the film passes perpendicularly through both blocks or panels of glass and also through the film. On their exterior surfaces the blocks of glass are exposed to air, but on their interior surfaces they are covered with the liquid, which also extends between the two blocks or panels so as to fully surround the film within the printing or projection chamber.
The total amount of liquid used in the aquarium gate is relatively small. A pair of seals are constructed at points just before and just after the aperture, and the liquid body is confined between the seals and the glass walls. This body of liquid does not remain static, but on the contrary there are inlet and outlet conduits which communicate with the liquid chamber, and the liquid is continuously pumped through the chamber and hence continuously flows over the surfaces of the film while the photographic operations are being carried out. One reason for providing continuous flow of the liquid is to minimize the probability that bubbles will enter the chamber; another is to carry away any particulate matter that may have entered with the film; and still a third reason is to eliminate thermoclines, a distortion effect that results from unequal distribution of heat energy within the liquid body.
In all of these types of prior art apparatus there has been a problem, which we have now come to recognize, and upon which our invention is based. This problem is that, while the liquid immersion apparatus functions very well from the beginning to the end of a particular reel or roll of film, it does not necessarily function well when changing to the next reel or roll.
When a new reel or roll of film is to be threaded into the machine, it is first necessary to withdraw the liquid or solvent from the printing or projection chamber. This is true because it is necessary to thread the next film into the machine in a dry state, in order to protect the operator from chemical effects of the solvent. This procedure has, apparently, been universally used throughout the industry. Unfortunately, however, withdrawal of the liquid or solvent exposes clean surfaces to the air, and provides a new opportunity for accumulation of particulate matter or other kinds of dirt. The necessary cleaning operations, and steps taken to avoid the dirt, have caused considerable down time of the apparatus while changing from one roll or reel of film to the next, and have also resulted in significant amounts of scrap or wastage when improperly performed.
The object and purpose of the present invention, therefore, is to extend the benefits of liquid immersion techniques to the change-over from one roll or reel of film to the next. More specifically, it is the object and purpose of the invention to make it unnecessary to engage in extensive cleaning of the apparatus before resuming the photographic operations.